Thursday, July 12, 2007

Cholesterol Production Via Carbohydrate Intake

Winthrop, and others, have asked me to explain how foods such as carbohydrates that don't contain cholesterol can affect cholesterol levels in the body. His question was prompted by my previous post, How To Avoid Filling A Statin Prescription, where I recommended reducing intake of processed carbohydrates.

Here's a bare-bones reply:

Cholesterol is a type of fat. It is a major component of fatty streaks or plaques that develop in arteries (see photo).

Most of the cholesterol in our body, 80-90%, is manufactured within cells in our body. Little comes from food we eat. If you stopped eating cholesterol entirely, you could still have high cholesterol levels.

The more cholesterol you eat, the less your body makes. The less cholesterol you eat, the more your body makes. (This is called a feedback mechanism.)

Cholesterol is made inside our cells from certain raw materials, and is instructed to be made by certain signaling molecules.

The raw material for cholesterol production (and triglyceride production) inside our cells is a 2-carbon molecule (Acetyl-CoA). That 2-carbon molecule can come from the breakdown of carbohydrate, fat, or protein.

Carbohydrates are built from a basic unit called a monosaccharide, which usually provides 6 carbons.

You can get a mother lode of 2-carbon fragments, the raw material for making cholesterol (and triglycerides), from the breakdown of starch.

When we eat carbohydrate, our body secretes the hormone insulin. When we eat a processed carbohydrate (whose glucose units are freed faster than those from a minimally processed carb, i.e. has a higher glycemic index) our body secretes proportionately more insulin.

Insulin is an anabolic or building hormone. Along with other signaling molecules, insulin controls the production of fats such as cholesterol and triglycerides (mostly increasing them). It also controls the packaging of cholesterol and triglycerides into LDL, VLDL, HDL, and other lipoproteins.

The combination of lots of raw material (carbohydrate, especially highly processed carb), and lots of insulin may result in higher levels of circulating cholesterol and triglycerides over time. That's one thought anyway.

The above mechanism is extremely basic. I'm humbled by my growing knowledge of these metabolic pathways - the number of feedback mechanisms, types of signaling molecules, influence of other health factors such as insulin resistance, metabolic syndrome, obesity, diabetes, as well as age, gender, genetics etc. - that I almost didn't post this. But I wanted to give an answer to a question I'm often asked. Consider this a very basic explanation. Cutting and pasting it into your take-home essay on cholesterol is a fool's risk.

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Photo of a human coronary artery with cholesterol-ridden plaque from the University of Pennsylvania School of Medicine.